Thermosetting coating composition comprising polymeric catalyst-II

ABSTRACT

A novel organic solvent based, thermosetting coating composition comprises novel epoxy ester resin having number average molecular weight (M n ) about 1000 to about 5000 and being the reaction product of diepoxide, for example bisphenol-A epichlorohydrin epoxy resin, with (i) dicarboxylic acid, for example the dimerization reaction product of C-18 fatty acid, in chain extension reaction and (ii) fatty acid, for example Soya fatty acid, in chain terminating esterification reaction, which chain extension reaction and esterification reaction occur at least in part substantially simultaneously. Preferably, catalyst is employed for said chain extension and esterification reactions. The coating composition further comprises polyfunctional aminoplast crosslinking agent, for example, hexamethoxymethylmelamine, and polycarboxy functional polymeric catalyst. Also provided is a method of making a humidity and solvent resistant coating on a substrate, adapted to provide corrosion protection to the substrate, for example, to bare sheet metal of an automotive vehicle body, which method comprises applying the novel coating composition of the invention to the substrate, for example, by spraying techniques, and subjecting the applied coating to an elevated temperature for a time sufficient to cure the coating.

TECHNICAL FIELD

This invention relates to a novel epoxy ester resin and to a novel,solvent-based, thermosetting coating composition comprising same. Itrelates also to such coating composition formulated, for example, assprayable, high solids coating composition suitable for use as anautomotive vehicle primer to make coatings which are highly resistant tocorrosion, humidity and solvents.

BACKGROUND ART

Solvent-based coating compositions are known which employ high molecularweight (e.g. 2,000 to 10,000) polymer resins having crosslinkingfunctionality, and a suitable crosslinking agent. Typically, suchcoating compositions are applied to a substrate, for example, byspraying, and are then cured by baking the coated substrate at anelevated temperature suitable to drive off the organic solvent and topromote the crosslinking reaction. The resulting thermoset coating, ifsufficiently humidity and solvent resistant, can provide aesthetic andfunctional advantages including corrosion protection for the underlyingsubstrate.

Coating compositions comprising such high molecular weight polymerresins typically comprise only 25% to 50% solids so as to be sprayableor otherwise conveniently applicable to a substrate. The viscosity ofcoating compositions of higher solids content is typically too high forthis purpose. Conventional epoxy ester based automotive vehicle sprayprimers, for example, typically have a volatile organic content ("VOC")of approximately 623 g/l (5.2 lb./gal).

Elimination of the volatile organic solvent portion during curing ofthese conventional low-solids coating compositions is relatively largeand therefore presents undesirable material handling difficulties, andadded expense. Furthermore, excessive solvent losses and/or solventrecovery equipment add considerable expense to the coating operation.Recently, governmental regulations on hydrocarbon emissions,particularly applicable to automotive coating operations, mandate asignificant reduction in volatile organic content for coatingcompositions. Thus, for example, in the United States, governmentalguidelines establish certain deadlines by which time emissions ofvolatile organics from automotive vehicle primer coating operations mustbe reduced to within certain defined limits. To meet such guidelines,coating compositions of reduced VOC can be employed in conjunction withemissions treatment equipment to achieve the specified emissions limit.Such treatment presents significant additional expense, however, andthus there is a great need for coating compositions of VOC reduced nearto, or preferably even lower than the governmental limits, which yet canbe applied to a substrate using known spray application techniques.

In response to these concerns, high solids coating compositions havebeen suggested which, typically, employ a low molecular weightmulti-functional adduct or copolymer in combination with amulti-functional crosslinking agent. These high solids coatingcompositions can be applied by spraying, for example, with lower VOCthan would be possible with conventional epoxy ester based coatingcompositions or other conventional coating compositions comprising highmolecular weight polymer resins. After application to the substrate,high solids coating compositions are cured by baking at a curetemperature, that is, at an elevated temperature suitable to drive offthe volatile organic content and to promote crosslinking and in someinstances polymerization of the multi-functional low molecular weightcomponent(s).

Typically, the physical properties of the coatings provided by suchknown high solids coating compositions can differ significantly fromthose of the cured coatings provided by the conventional, low solidscoating compositions. In particular, the cured coatings obtained fromknown high solids coating compositions can be inferior in that they canbe less flexible, less solvent resistant, less adherent to the substrateand/or for other reasons provide less corrosion inhibition for theunderlying substrates. Accordingly, it would be highly desirable toprovide a coating composition comprising low molecular weight materialssuitable for use in high solids, solvent based coating compositions andyet which, upon curing, form coatings having physical propertiescomparable to those obtained from conventional low solids solvent-basedcoating compositions.

Accordingly, it is an object of the present invention to provide novellow molecular weight resins suitable for use in high solids,solvent-based thermosetting coating compositions. In this regard, it isa particular object of the invention to provide novel low molecularweight epoxy ester resins which are crosslinkable during cure, on thesurface of a substrate.

It is another object of the invention to provide novel coatingcompositions comprising such crosslinkable epoxy ester resins. In thisregard, it is a particular object of the invention to provide a novelepoxy ester thermosetting coating composition of sufficiently low VOC tomeet governmental guidelines and yet which can be applied to a substrateby spraying or other known method.

It is another object of the invention to provide a method of making acoating on a substrate, which coating has advantageous physicalproperties including, for example, humidity and solvent resistance andcorrosion protection for the underlying substrate. Additional aspectsand advantages of the invention will be apparent from the followingdescription thereof.

DISCLOSURE OF THE INVENTION

According to the present invention, a novel organic solvent basedthermosetting coating composition comprises

A. epoxy ester resin of number average molecular weight (M_(n)) about1000 to about 5000, being the reaction product of diepoxide with (i)dicarboxylic acid in chain extension reaction and (ii) fatty acid inchain terminating esterification reaction, which chain extensionreaction and esterification reaction occur substantially simultaneouslyat a reaction temperature reaching at least about 135° C., wherein theepoxy functionality, dicarboxylic acid carboxyl functionality and fattyacid carboxyl functionality are employed in relative proportions ofabout 1:0.3-0.8:0.3-0.8 equivalents, respectively;

B. polyfunctional aminoplast crosslinking agent; and

C. polycarboxy functional polymeric catalyst of number average molecularweight (M_(n)) about 1,000-10,000 being substantially unreactive at roomtemperature with the epoxy ester resin and the polyfunctional aminoplastcrosslinking agent, in an amount of about 2% to about 15% by weight ofresin solids in the coating composition.

Particularly preferred compositions of the invention are thoseformulated as high solids coating compositions adapted to be applied byspraying onto a substrate. Such compositions are especially useful as aprimer coat on the bare, unpolished metal surface of an automotivevehicle body. As used herein, a high-solids coating composition is onein which a volatile organic content of about 400 g/l (3.4 lb./gal.) orless yields a viscosity of less than approximately 35 sec. #4 Ford Cupat 27° C. (80° F.).

According to another aspect of the invention, a method of making acorrosion, solvent and humidity resistant coating on a substratecomprises applying to the substrate the novel, solvent based,thermosetting coating composition of the invention and subsequentlysubjecting the coating to an elevated temperature for a time periodsufficient to substantially cure the coating layer. Typically, the novelcoating compositions of the invention can be cured by heating to betweenabout 100° C. (212° F.) and about 230° C. (445° F.), for a time periodsufficient to yield a cured coating, for example for about 15 to about60 minutes. According to preferred embodiments of the invention, thecoating composition can be sufficiently cured for good coatingproperties by heating to about 120° C. (250° F.) for about 15 minutesbut, in addition, such preferred composition will tolerate curing at upto about 200° C. (392° F.) for as much as about 60 minutes withoutsubstantial lose of such advantageous coating properties.

The coating compositions of the present invention have been foundespecially advantageous for use as high solids primer compositionssuitable to be applied by spraying techniques. More specifically, highsolids coating compositions according to the invention, formulated, forexample, at VOC as low as about 407 g/l (3.4 lb./gal.) to about 503 g/l(4.2 lb./gal.) are found to have viscosity as low as about 15 to about45 sec., #4 Ford Cup at 27° C. and are well suited to spray applicationtechniques. High solids coating compositions according to preferredembodiments are found to have viscosity as low as about 15 sec. to about25 sec., #4 Ford Cup at 27° C., at VOC of about 407 g/l to about 443 g/l(3.4 to 3.7 lb./gal.). Accordingly, the coating compositions of theinvention provide ease of material handling and less expense thanpreviously known coating compositions which were sprayable only athigher VOC. Furthermore, the coating compositions of the invention canbe used to meet or exceed governmental guidelines regarding hydrocarbonemissions with a reduction or elimination of emissions treatment andemissions treatment equipment. In addition, reduction in the amount ofhydrocarbon solvent used in the coating composition provides direct costadvantage.

Unlike various previously suggested high solids coating compositions,the coating compositions of the present invention provide theabove-mentioned low VOC and cure-response advantages without sacrificeof advantageous physical properties in the cured coating. On thecontrary, when applied, for example, over a metallic substrate, such aswhen applied as an automotive vehicle primer coat over bare sheet steel,cured coatings according to the invention have been found to provideexcellent adhesion to the substrate, excellent humidity resistance, andexcellent corrosion resistance in comparison to other commerciallyavailable high solids coating compositions of similar nature.

Other features and advantages of this invention will become moreapparent from the succeeding, detailed description thereof including thepreferred embodiments and best mode of carrying out this invention.

DETAILED DESCRIPTION OF THE INVENTION

The epoxy ester resin employed in the coating composition of theinvention is the reaction product of a diepoxide with (i) dicarboxylicacid and (ii) fatty acid, such as Soya fatty acid. It is a significantcharacterizing aspect of the invention that the chain-extension reactionof the diepoxide with the dicarboxylic acid is carried out substantiallysimultaneously with the chain-termination esterification reaction of thediepoxide with the fatty acid. While not wishing to be bound by theory,it is presently understood that the esterification reaction of thecarboxyl functionality of the fatty acid with the epoxy functionality ofthe diepoxide proceeds at very nearly the same or similar rate as thechain extension reaction of the carboxyl functionality of thedicarboxylic acid with the epoxy functionality, given the reactionconditions of the invention as specified herein. Likewise, reaction ofthe hydroxyl functionality, generated by the aforesaid chain-extensionand chain termination reactions, with the carboxyl functionality of thefatty acid would proceed at very nearly the same or similar rate as thereaction of such hydroxyl functionality with the carboxyl functionalityof the dicarboxylic acid. Carrying out these reactions simultaneouslyproduces a resin comprising a variety of different molecular structures,not merely a series of analogs of the same structure. In addition,simultaneous reaction appears to yield a product epoxy ester resin ofexceptionally wide molecular weight distribution such as, for example,from about 600 or less to about 12,000 or more. A significant advantageof the invention, which is presently understood to stem, in part, fromthe simultaneous reaction, and particularly from the wide molecularweight distribution of the epoxy ester resin product, is thesurprisingly low viscosity of the coating compositions comprising theseresins. More specifically, the coating compositions of the invention arefound to have a significantly lower viscosity at a given solids content(by weight) than many comparable, commerically available high solidscoating compositions. Accordingly, the coating composition of theinvention can be sprayed at significantly higher solids content and,thus, require significantly lower VOC.

It is seen to be another consequence of the wide molecular weightdistribution of the novel epoxy ester resin of the invention that theglass transition temperature (Tg) of the epoxy ester resin isadvantageously low. More accurately, it is presently understood that thelower molecular weight fraction of the epoxy ester resin and anyunreacted monomer act in the nature of a plasticizer for the resin toeffectively provide a lower apparent Tg. In any event, it is significantthat such low Tg is achieved, since low Tg is well known to provide animproved, smoother surface on the cured coating. During heating to curethe coating, after it reaches its Tg and before it substantially curesat its cure temperature, the coating can flow and become smooth. Thus,the lower Tg provides a longer time period during which the coating canflow and become smooth and thus improve the surface quality of the curedcoating. In addition, the wide molecular weight distribution of theepoxy ester resin components is believed to contribute, in part, to theadvantageous flexibility of the cured coating of the invention. Thiscoating flexibility is also believed to stem, in large measure, from thehigh aliphatic content of the epoxy ester resins of the inventionaccording to preferred embodiments discussed further below, whereinaliphatic dicarboxylic acid is employed.

The diepoxide reactant suitable for the epoxy ester resin can be any ofnumerous diepoxides including many which are commercially available andwhich will be apparent to the skilled of the art in view of the presentdisclosure. While, ultimately, the choice of reactants for preparing theepoxy-ester resin will depend to an extent upon the particularapplication intended for the coating composition, terminal diepoxides,that is diepoxides bearing two terminal epoxide groups, are generallymost preferred. These are generally more reactive and therefore requirereaction conditions under which undesirable side reactions, for example,epoxy-epoxy reactions and gellation, can be more easily avoided.Preferably, the diepoxide has a number average molecular weight (M_(n))between about 100 and about 1000, and more preferably between about 100and about 600. Numerous such preferred diepoxides are readilycommercially available, for example, bisphenol-A epichlorohydrin epoxyresin, for example, the Epon (trademark) series, Shell Chemical Company,Houston, Tex., and the DER (trademark) series, Dow Chemical Company,Midland, Mich. Also preferred are cycloaliphatic diepoxy resins, forexample, the Eponex (trademark) series, Shell Chemical Company, Houston,Tex., hydantoin epoxy resins such as, for example, Resin XB2793(trademark), Ciba-Geigy Corporation, Ardsley, N.Y., and any of a widevariety of acyclic or cyclic aliphatic diepoxides such as, for example,1,4-butanediol diglycidyl ether and 4-vinylcyclohexene dioxide and thelike. Among those listed, diglycidyl ether bisphenol-A resins or highermolecular weight analogs thereof, are most preferred in view of theircost and commercial availability, for example, Epon 828 (trademark) andEpon 829 (trademark), of the Epon (trademark) series mentioned above.The higher molecular weight members of the Epon (trademark) series aresuitable for use where higher molecular weight epoxy ester resins aredesired. Generally, however, such higher molecular weight resins providecoating compositions of somewhat higher viscosity (or lower solidscontent). Additionally, it should be recognized that the highermolecular weight members of the Epon series, for example Epon 1001 andEpon 1004, may be somewhat less preferred, since these bear hydroxylfunctionality which may undergo undesirable side reactions with, forexample, epoxy functionality. The result can be undersirable resinproperties and gellation. Other suitable diepoxides for use insynthesizing the epoxy-ester resin of the invention are commerciallyavailable and will be apparent to the skilled of the art in view of thepresent disclosure. Also, it will be understood from the foregoing thatany mixture of compatible diepoxides may be used.

In addition to the diepoxide, a portion of the epoxy functionality canbe provided by any compatible monoepoxy compound or, more suitably,polyepoxy compound or mixture of compounds having three or more epoxygroups per molecule. Suitable such polyepoxides include, for example,those of molecular weight about 200 to about 800. The polyepoxide can beessentially any of the well known types such as polyglycidyl ethers ofpolyphenols. These can be produced by etherification of a polyphenolwith epihalohydrin in the presence of alkali. It will be recognized bythe skilled of the art in view of the present disclosure, that in someinstances, particularly where a coating composition of high solidscontent is less important, it may be desirable to employ polyepoxideshaving higher molecular weights. Preferably, any such polyepoxidecontains free hydroxyl groups in addition to epoxide groups.

While polyglycidyl ethers of polyphenols can be employed, it isfrequently desirable in such compositions to react a portion of thereactive sites (hydroxyl or in some instances epoxy) with a modifyingmaterial to vary the film characteristics of the resin. The epoxy resinmay be modified, for example, with isocyanate group containing organicmaterials or other reactive organic materials.

Another quite useful class of polyepoxides are the Novolak resinsincluding, for example, the Novalak epoxy resins ECN 1235 (trademark)and ECN 1273 (trademark), Ciba-Geigy Corporation.

According to preferred embodiments of the present invention, epoxidecompounds other than diepoxide compounds provide no more than about 15%and most preferably substantially none of the total epoxidefunctionality in the reactants used to form the epoxy-ester resin.

The dicarboxylic acid reactant suitable for the epoxy ester resin of thepresent invention includes numerous commercially available materials,many of which will be readily apparent to the skilled of the art in viewof the present disclosure. Suitable dicarboxylic acids include saturatedor unsaturated, cyclic or acyclic aliphatic or aromatic dicarboxylicacids or a mixture thereof. Acyclic aliphatic dicarboxylic acids aregenerally preferred in view of the enhanced flexibility they provide tothe cured coatings of the invention. Preferred dicarboxylic acids havethe general formula (I):

    HOOC--R--COOH                                              (I)

wherein R is a divalent linking moiety substantially unreactive with thediepoxide resin. It will be apparent to the skilled of the art in viewof the present disclosure that R should be substantially unreactive alsowith the fatty acid employed for the epoxy ester resin, with hydroxyfunctionality (generated in the chain-extension reaction) and, at leastat storage temperatures, with the crosslinking agent and polymericcatalyst employed in the coating composition. Preferably R is adivalent, organic, linking moiety. Particularly preferred are thosedicarboxylic acids where R is selected from the group comprising astraight or branched alkylene or alkylidene moiety, preferably of about4-42 carbons, for example, (CH₂)_(n) where n is preferably from about 4to about 42, and the like, or a mixture thereof. Dicarboxylic acids ofthis character have been found to provide good reactivity with thepreferred diepoxides described above and to provide, ultimately, curedcoatings of the invention having excellent physical properties, mostnotably excellent corrosion protection. Preferably the dicarboxylic acidhas a number average molecular weight (M_(n)) between about 145 andabout 1000, more preferably about 570. Dicarboxylic acids within thisrange, employed with the preferred diepoxides described above andsuitable fatty acid, are found to provide epoxy ester resins comprisingmixed reaction products of particularly wide molecular weightdistribution, which resins (as discussed above) are found to providecoating compositions of the invention having especially advantageousphysical properties including low Tg and good corrosion protection.

Exemplary dicarboxylic acids include adipic acid,3,3-dimethylpentanedioic acid, benzenedicarboxylic acid,phenylenediethanoic acid, naphthalenedicarboxylic acid, pimelic acid,suberic acid, azelaic acid, sebacic acid, and the like or a compatiblemixture of any of them. While dicarboxylic acids according to formula(I) can be used, wherein R is an alkylene chain of less than 4 carbons,for example, oxalic acid, malonic acid, succinic acid, glutaric acid andthe like, these are less preferred in view of the somewhat lesser degreeof flexibility provided thereby.

Preferably the dicarboxylic acid provides two terminal carboxyl groups.Similarly, preferred aromatic dicarboxylic acids are those wherein thecarboxylic groups are more spaced apart, for example,1,4-benzenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid.

The most preferred dicarboxylic acids are substantially saturated,acyclic, aliphatic dimer acids, which are well known to the skilled ofthe art and readily commercially available. These are typically thedimerization reaction products of fatty acids which have from 4 to 22carbons and a terminal carboxyl group. Of these, dimer acid of 36carbons is most preferred since it provides excellent reactivity withthe preferred diepoxides described above, provides epoxy ester reactionproducts of advantageously wide molecular weight distribution, andprovides, ultimately, cured coatings of the invention having excellentphysical properties. In addition, dimer acid of 36 carbons is readilycommercially available, for example, as Empol 1014 (trademark), Empol1016 (trademark) and Empol 1018 (trademark), each available from EmeryIndustries, Inc., Cincinnati, Ohio. It should be recognized that most orall commercially available dimer acid contain some portion of trimeracid, typically, for example, about 5-10% but in some cases as much as30% or more, and also contain a usually smaller portion ofmonocarboxylic acid. As used herein, the term "dimer acid" includesthose containing such amounts of these materials. Most useful in thepresent compositions are products that contain mostly dibasic acid andnone or low amounts of tribasic and monobasic acids.

Aliphatic dicarboxylic acids are seen to provide additional advantages.In particular, while not wishing to be bound by theory, it is presentlyunderstood that the epoxy ester resins derived therefrom wet thesubstrate surface better and provide enhanced adhesion between thesubstrate and the cured coating. They also flow better and, thus,provide an excellent smooth surface upon being cured. Also, thealiphatic units provide enhanced flexibility to the cured coating, asnoted above, and this flexibility is seen to provide enhanced impactresistance. In this regard, it is presently understood that in the epoxyester resins according to preferred embodiments, employing aliphaticdicarboxylic acid and aliphatic fatty acid, the molecular weightdistribution is exceptionally wide due to the approximately identicalreaction rates of these reactants with the diepoxide. Such exceptionallywide molecular weight distribution further enhances the flexibility ofthe cured coating.

Where corrosion protection for the substrate is important, it may bepreferred to employ dicarboxylic acid according to formula (I) above,wherein R is, at least in part, aromatic. It is believed that sucharomatics in the coating composition of the invention, such as a primercomposition for a metal substrate, are more resistant to hydrolysis thanare aliphatics and, therefore, provide enhanced corrosion and moistureresistance. Of course, according to preferred embodiments of the epoxyester resin described above, the diepoxide reactant provides aromaticunits to the resin and this would similarly contribute to corrosion andmoisture resistance. Other dicarboxylic acids suitable for the epoxyester resin of the present invention will be apparent to the skilled ofthe art in view of the present disclosure.

The fatty acid employed as a chain terminating esterification reactantfor the epoxy ester resin of the present invention includes numerouscommercially available materials. Suitable fatty acids include thosederived from or contained in either animal or vegetable fat or oil.Preferred are fatty acids of from about 8 to about 18 carbons. Alsopreferred among the fatty acids are the more saturated fatty acids,since it appears that olefinic unsaturation in the fatty acid canundergo a polymerization-type reaction between such double bonds duringthe synthesis of the epoxy ester resin of the invention. Unsaturatedfatty acids are suitable for use, however, such as, for example, oleicacid, linoleic, linolenic or the like and mixtures of those acids, andcan be used together with a suitable inhibitor for thepolymerization-type reaction such as hydroquinone or the like, of whichmany are commercially available and will be apparent to the skilled ofthe art in view of the present disclosure. In addition, aromatic fattyacids are commercially available and can be employed. The aliphaticfatty acids are preferred, however, in view of the enhanced coatingflexibility they provide. Especially preferred for use are thesubstantially saturated, acyclic aliphatic fatty acids such as Soyafatty acid which is most preferred, and butyric, lauric, palmitic andstearic fatty acids and the like or a mixture of any of them. These arerelatively inexpensive and have been found to provide good reactivitywith the preferred diepoxides described above. For convenience of use,the fatty acids which are semisolid or liquid at room temperature aregenerally preferred over the solid fatty acids.

The epoxy ester resin of the invention can be made according to reactionconditions now specified, employing techniques which are well known andwhich will be readily apparent to the skilled of the art in view of thepresent disclosure. The chain extension and chain termination reactionsoccur substantially simultaneously by charging the diepoxide, thedicarboxylic acid and the fatty acid in a suitable reactor and heatingthe mixture. It should be recognized that to assure rapid and/or morecomplete reaction of the diepoxide with the carboxylic moieties of thedicarboxylic acid and of the fatty acid, and to assure that thesereactions occur substantially simultaneously, that is, that they proceedsubstantially concurrently at approximately the same or similar rates,it is usually preferred to have a catalyst present. Alternatively, othertechniques, for example, higher reaction temperatures and/or longerreaction times can be used to provide substantially simultaneous, rapidand complete reactions. While not a serious concern if the dicarboxylicacid consists of the preferred dimer acids discussed above, in the caseof certain dicarboxylic acids greatly differing from the fatty acidemployed in the reaction, reaction temperatures below about 135° C.(280° F.) may result in the rate of reaction of the fatty acid with thediepoxide being significantly different from the rate of reaction of thedicarboxylic acid with the diepoxide. In these instances, the use ofcatalyst is preferred. Epon 829 (trademark), mentioned above, as sold,provides a proprietary catalyst. Epon 828 (trademark), is substantiallythe same but does not provide such catalyst. Suitable catalysts arecommercially available and include, any of the well known catalysts forepoxy-carboxylic reactions such as, for example, sodium carbonate whichis preferred, and lithium neodecanoate, lithium naphthenate, lithiumnanoate, other known organometallic catalysts and tertiary aminecatalysts and the like or a compatible mixture of any of them. Otherswill be apparent to the skilled of the art in view of the presentdisclosure.

The reaction mixture is generally heated, in the presence of catalyst,to at least about 135° C. (280° F.), preferably at least about 150° C.(300° F.). Typically, the reaction mixture is heated to about 170°-190°C. (340°-370° F.). An exothermic reaction is observed and the progressof the reaction can be followed by measuring acid number. After the acidnumber measurements have indicated the reaction is sufficientlycompleted, preferably at acid number 7 or less, the resin may be dilutedwith suitable solvent in order to reduce the viscosity to a desirablelevel. A non-volatile contents level of 80% has been found to besuitable for storage of the coating composition.

Since, in the preferred embodiments described above, the chain extensionreaction of the epoxide functionality with the dicarboxylic acidproceeds at very nearly the same rate as the chain termination reactionof the epoxide functionality with the fatty acid, and since these tworeactions are carried out simultaneously to yield the epoxy ester resin,it would be recognized that the relative proportions of the reactants inthe reaction mixture can significantly effect the properties of theproduct resin. Accordingly, it has been found that the reactants arepreferably present in amounts which provide the reactive functionalityin the relative proportions of one equivalent of epoxy functionality, toabout 0.3 to about 0.8 equivalent of dicarboxylic acid carboxylfunctionality, to about 0.3 to about 0.8 equivalent of fatty acidcarboxyl functionality. More preferred relative proportions are oneequivalent of epoxy functionality to about 0.4-0.6 equivalent ofdicarboxylic acid carboxyl functionality, to about 0.4-0.6 equivalent offatty acid carboxyl functionality. Most preferably diepoxide,dicarboxylic acid and fatty acid are employed in relative amounts ofapproximately 1:0.4:0.5 equivalents of functionality, respectively. Onemost preferred embodiment employs the reaction product of digylcidylether bisphenol-A resin with (a) the dimerization reaction product ofC-18 fatty acid and (b) Soya fatty acid, in relative proportions ofabout 1:0.5-0.7:0.7-0.9 be weight, respecitively. Epoxy ester resinsprovided according to these preferred ranges of reactant amounts havebeen found to provide coating compositions having exceptional physicalproperties, most especially corrosion protection such as, for example,when (spray) applied to a metal substrate such as, for example, bare,unpolished automotive vehicle body sheet steel.

The above described epoxy ester resin is employed together withpolyfunctional aminoplast crosslinking agent. Included within thecrosslinking agents suitable for use in the coating composition arenumerous materials which are well known to the skilled of the artincluding, for example, alkylated melamine formaldehyde resins with oneto about eight carbon atoms in the alkyl group. Other suitablecrosslinking agents will be apparent to the skilled of the art in viewof the present disclosure. Many such crosslinking agents are readilycommercially available including, for example, the Resimene (trademark)series, Monsanto Company, St. Louis, Mo., the most preferred beingResimene 717 (trademark), described as a low temperature cure methylatedmelamine-formaldehyde resin.

In addition, suitable polyfunctional aminoplast crosslinking agents canbe prepared employing conventional techniques. Accordingly, for example,a lower alkanol such as methanol, ethanol, butanol, isobutanol,isopropanol, hexanol, 2-ethylhexanol or the like or a mixture of any ofthem is reacted with a melamine formaldehyde. Preferred crosslinkingagents of this type include butylated melamine formaldehyde resin,methylated/butylated formaldehyde resin and polyalkyl ethers ofpolymethylol melamines and the like, of which hexamethoxymethyl melamineresin is most preferred in view of its relatively lower cost, readycommercial availability, its low reactivity with the epoxy ester resinof the invention at normal storage temperatures and its high reactivityat elevated cure temperatures. In this regard, preferred polyfunctionalaminoplast crosslinking agent is substantially unreactive with the epoxyester resin at or below about 60° C. Other suitable melaminecrosslinking agents will be apparent to the skilled of the art in viewof the present disclosure.

The proper proportion of polyfunctional aminoplast crosslinking agent toepoxy ester resin will depend, in part, upon the properties desired inthe coating to be produced and, in part, upon the desired cure responseof the coating composition (which will depend, in turn, upon the bakingschedule intended for curing the coating composition) and, in part, uponthe desired storage stability of the coating composition, that is, uponthe desired shelf life. Accordingly, the amounts of epoxy ester resinthat can be blended with the crosslinker to form coating compositions ofthe invention may be varied considerably. Preferably, the crosslinkingagent is used in amounts of about 5% to about 40% by weight of the totalresin solids, more preferably about 20% to about 30%.

The use of polycarboxy functional polymeric catalyst as a component ofthe coating composition of the invention is a novel and significantlyadvantageous aspect of the present invention. It can be made accordingto conventional polymerization processes well known to the skilled ofthe art, such as batch polymerization. Accordingly, the polymericcatalyst can be made, for example, by conventional techniques in whichthe monomers, solvents and polymerization initiators are charged into areaction vessel and heated to a polymerization temperature forsufficient time to form the copolymer. Preferably, the monomers and apolymerization initiator, for example t-butyl perbenzoate, are firstmixed together, optionally with a small quantity of solvent, and thenadded slowly, for example over several hours, to refluxing solventcontaining additional polymerization initiator. The polymerizationinitiator in the refluxing solvent can be one different from butcompatible with the initiator mixed with the monomers, for example,cumene hydroperoxide. Other suitable polymerization initiators are wellknown and will be apparent to the skilled of the art in view of thepresent disclosure. Preferably the polymeric catalyst is stored in lineddrums, since it has been found to be somewhat incompatible with steel.

The polymeric catalyst may comprise any suitable polycarboxy functionalmaterial which is compatible with the other components of the coatingcomposition. In general, the polymeric catalyst can be any polycarboxyfunctional compound or mixture of compounds substantially unreactivewith the epoxy ester resin and the polyfunctional aminoplastcrosslinking agent at storage conditions, (that is, typically, at roomtemperature). Preferably, the polymeric catalyst has a number averagemolecular weight (M_(n)) about 1,000-10,000, more preferably about 1,500to about 3,000. While use of polymeric catalyst of higher number averagemolecular weight, for example, about 10,000, is found to produce coatingcompositions of somewhat higher viscosity, when used in suitableamounts, for example about 2-5% by weight of epoxy ester resin, it ispossible to employ same to prepare high solids coating compositions.According to preferred embodiments, the polymeric catalyst comprises thepolymerization reaction product of (i) suitable ethylenicallyunsaturated carboxylic acid, that is, carboxylic acid providing a doublebond for polymerization such as, for example, acrylic acid, methacrylicacid, which two are preferred, butanoic acid and the like or acompatible mixture of any of them, with (ii) any suitable ethylenicallyunsaturated copolymerization monomer providing a double bond forpolymerization and which provides to the polymerization reaction productno functionality substantially reactive with the epoxy ester resin orthe polyfunctional crosslinking agent of the coating composition atstorage temperature. According to such preferred embodiments, thepolycarboxy functionality is introduced into the polymer as pendantgroups on the polymer backbone by copolymerizing the carboxylic acidwith the copolymerization monomer.

Suitable copolymerization monomers include, for example, alkyl acrylatesand alkyl methacrylates having 1 to about 8 carbons, preferably about1-4 carbons, in the alkyl group. Typical alkyl acrylates that can beused to prepare the polymeric catalyst are methyl acrylate, ethylacrylate, propyl acrylate including, for example, isopropyl acrylate,any butyl acrylate, hexyl acrylate, 2-methylpentyl acrylate, octylacrylate and the like or a mixture of any of them. Generally preferredare butyl acrylate, butyl methacrylate or a mixture of them. Preferredcopolymerization monomers include butyl methacrylate, which is generallymost preferred, glycidyl acrylate, glycidyl methacrylate, styrene, anysuitable vinyl ethers, and the like or a compatible mixture of any ofthem. Suitable carboxylic acids and copolymerization monomers inaddition to those recited above are commercially available and will beapparent to the skilled of the art in view of the present disclosure.

According to certain preferred embodiments of the invention, thepolymeric catalyst is the reaction product of about 55% to about 80% byweight, preferably about 70% by weight copolymerization monomers withabout 20% to about 45%, preferably about 30% by weight carboxylic acidmonomers.

One preferred polymeric catalyst according to the invention consists ofthe polymerization product of about 30% by weight acrylic acid withabout 70% by weight butyl methacrylate. The polymerization reaction ispreferably carried out in the presence of initiator such as t-butylperbenzoate and cumene hydroperoxide or the like. A suitable procedurefor making this and other polymeric catalyst of the invention isdetailed in the Examples, below.

The amount of polymeric catalyst used in the coating composition of theinvention depends, in part, upon the desired cure response and, in part,upon the physical properties desired in the cured coating. Sufficientpolymeric catalyst is used to provide significant improvement in thephysical properties of the cured coating while maintaining the coatingcomposition sufficiently storage-stable for its intended use. It shouldbe noted, however, as further discussed below, that it is a significantadvantage of the present invention that the coating compositions are farmore storage-stable with the polymeric catalyst than are likecompositions containing an equivalent amount of known, non-polymericcatalyst. It should be noted, in addition, that the coating compositionsof the invention can employ a portion, preferably a minor portion, ifany, of the known, non-polymeric catalysts in conjunction with theabove-described polymeric catalyst. Such non-polymeric catalysts knownto the skilled of the art to catalyse the aminoplast crosslinkingreaction include, for example, p-toluenesulfonic acid, phosphoric acid,phenyl acid phosphate, butyl phosphate, butyl maleate, and the like or acompatible mixture of any of them. These catalysts are known to be mostuseful for coating compositions intended for low temperature curingschedules and/or when highly etherified melamine resins are used such ashexa(methoxymethyl)melamine or the like and are used in amounts whichdepend, in part, upon the intended baking (curing) schedule. (Typically,amounts of about 0.2% to about 3.0% by weight of total resin solids areused.) In the present invention, it is most preferred that thepolycarboxy functional acrylic copolymer catalyst be used without suchaddition, non-polymeric catalyst.

While it will be within the skill of the art in view of the presentdisclosure to determine the most suitable amount of polymeric catalystto be used in a coating composition of the invention intended for agiven use, it typically will be preferred to use sufficient polymericcatalyst to raise the acid level of the epoxy ester resin as high asabout 50, more preferably about 15 to about 35. Generally preferred isuse of polymeric catalyst in amounts of about 2-10% by weight of resinsolids in the coating composition. In the preferred embodiment of thecoating composition of the present invention, about 5-10% polymericcatalyst has been found to be more preferred, and about 8% mostpreferred. Although up to 15% or more can be usefully employed, suchamounts may not provide the full advantage of storage stability providedby use of more preferred amounts. The polymeric catalyst can be added tothe epoxy ester resin by any known mixing method. Preferably, however,it is "hot blended", that is, it is mixed with the epoxy ester resin atelevated temperature, for example at or above about 105° C. (220° F.).Mixing at room temperature produces a somewhat cloudy coatingcomposition, while, surprisingly, mixing at elevated temperature isfound to produce a clear coating composition. The hot blended clearcoating composition has unexpectedly been found to provide a curedcoating of higher gloss than the cold blended cloudy composition. Ofcourse, where higher gloss is not desirable, it may be preferred to coldblend the resin and catalyst to avoid the added time and expense ofheating same.

As noted above, the polymeric catalyst component of the presentinvention is a significantly advantageous aspect of the presentinvention. More specifically, it has been found to increase the storagestability of the epoxy ester resin coating compositions over that oflike resin coating compositions employing known non-polymeric catalyst.Thus, for example, coating compositions according to preferredembodiments of the invention can be subjected to about 60° C. forperiods of about 24 hours with only small increase in viscosity, forexample, an increase of less than about 5 sec., #4 Ford Cup at 27° C.And even when subjected to temperatures of about 60° C. for periods ofabout 120 hours, preferred embodiments of the coating composition arefound to increase in viscosity less than about 10 sec., #4 Ford Cup at27° C.

Surprisingly, in addition to improved storage-stability, the coatingcomposition of the invention comprising polycarboxy functional polymericcatalyst can be cured at advantageously low temperatures. Thus, coatingcompositions of the invention can be cured within about 15-30 minutes attemperatures as low as about 135° C.-165° C. and yet yield substantiallyoptimal properties. In fact, even when the coating composition of thepresent invention is cured at such lower temperatures, the physicalproperties of the coating are improved over those achieved at highercure temperatures by some previously known high solids coatingcompositions employing known, non-polymeric catalysts. Specifically, forexample, the present invention, especially according to preferredenbodiments, provides excellent humidity resistance, corrosionresistance, hardness, gloss and acid resistance. These advantages areillustrated in the Exles below. Typically, it is most preferred to cureat about 150° C. for about 20 minutes.

In addition to both improved storage stability and the ability to cureat reduced temperature, the coating compositions of the invention havebeen found to be able to provide a cured coating of advantageousphysical properties when cured at any of a wide range of curetemperatures. More specifically, while, as noted above, the coatingcompositions according to preferred embodiments of the invention havebeen found to cure at advantageously low temperatures within shortcuring periods, yet, in addition, according to another highlyadvantageous aspect of the invention, the coating compositions can becured without significant loss of advantageous physical properties attemperatures as high as about 193° C. (380° F.) or more for periods upto about 60 minutes or more. Considered together with the storagestability of the coating composition, it can be readily recognized thatthe present invention provides a highly significant advance in thecoating composition art. More specifically, it can be seen that greatflexibility is provided by the coating compositions of the invention inboth designing and implementing a curing schedule for the coatingcomposition.

It will be within the skill of the art to determine the proper volatileorganic content for a given coating composition of the invention and fora given application. Preferred solvents have relatively low volatilityat temperatures appreciably below their boiling points such that solventevaporation is low during storage and/or application of the coatingcomposition to the substrate. A suitable solvent system may include, forexample, toluene, methyl ethyl ketone, isobutyl acetate, xylene,cellosolve acetate, acetone and a mixture of any of them. Other solventswhich may be employed include terpenes, aliphatic and aromatic naphthas,and the like. Additional suitable solvents are commercially availableand will be apparent to the skilled of the art in view of the presentdisclosure. Generally it is preferred to employ a portion of C-4 to C-8alcohol solvents such as, for example, butanol, pentanol, hexanol, andthe like or a mixture of any of them since these inhibit thecrosslinking reaction of the polyfunctional aminoplast resin with theepoxy ester resin at room temperature and thereby improve storagestability. At elevated temperature during cure, the alcohol solventevaporates and, hence, ceases to inhibit the crosslinking reaction.Preferred solvents also may include, for example, methyl amyl ketone andthe like, or a mixture thereof with C-4 to C-8 alcohol such as, forexample, a 1:2 mixture by weight of butanol and methyl amyl ketone,respectively which is generally most preferred.

Any solvent allowed to remain in the cured coating should be inert so asto avoid adverse effect upon the cured coating or upon another coatinglayer used in conjunction with it during the curing process orthereafter. Preferrably, the cured coating is substantially free ofsolvent.

Sufficient solvent is used to reduce the viscosity of the coatingcomposition to a level suitable for storage or for application to thesubstrate in the desired manner. While conventional epoxy esterautomotive spray-applied primer coating compositions are known torequire a volatile organic content of about 540 g/l, comparable coatingcompositions of the present invention require as little as 430 g/l orless VOC to provide a viscosity of about 18 sec., #4 Ford Cup at 27° C.(80° F.), which is suitable for spray application techniques. It isgenerally preferred that sufficient solvent be used to provide aviscosity of about 18 to about 22 seconds, #4 Ford Cup at 27° C. (80°F.) for a coating composition which is to be sprayed onto a substrate.Of course, the coating compositions of the invention need not beformulated as a "high solids" composition. Rather, it can have a higherVOC to provide a lower viscosity. Similarly, the coating compositions ofthe invention need not be formulated as a sprayable composition. Rather,it can have an even higher solids content and viscosity.

In addition to the epoxy ester rein, polyfurnctional aminoplastcrosslinking agent and polycarboxy functional catalyst, other componentscan be used, such as flow control agent(s), for example, polybutylacrylate; wetting agent(s), for example, silicone; pigments; pigmentdispersants; corrosion inhibitors, for example, chromate pigments,numerous of all of which are known to the skilled of the art. Inaddition, suitable reactive additives can be used, including, forexample, low molecular weight diol flow control agents and reactivediluents.

According to another aspect of the invention, a coating on a substrateis provided, which coating comprises the crosslinked polymer productfollowing cure of a coating composition of the invention. The coatingcomposition can be a low solids composition, that is, it can have a highVOC, but generally a high solids composition, that is, one having a lowVOC is preferred for the reasons given above. It can be applied by anyconventional method, including brushing, dipping, flow coating,spraying, etc. Spraying will generally be preferred, for example, forapplying the compositions as an automotive primer. For the reasonsdiscussed above, the novel epoxy ester resins of the invention areespecially advantageous for formulating high solids coatingcompositions. For this purpose, the epoxy ester resin of the inventionpreferably has a number average molecular weight (M_(n)) of about 1000to about 3000. In this regard, coating compositions of the inventionemploying preferred epoxy ester resin, preferred crosslinking agent andpreferred polymeric catalyst, as described above, are suitable to beapplied to a substrate by spraying even though formulated at volatileorganic content levels as low as about 347-467 g/l (2.9-3.9 lb./gal.), amore preferred range being about 395-467 g/l (3.3-3.9 lb./gal).

Curing the coating composition requires baking for sufficient time atsufficiently elevated temperature to react the crosslinking agent withthe epoxy ester resins. The time and temperature required to cure thecoating are interrelated and depend upon the particular epoxy esterresin, crosslinking agent, polymeric catalyst, solvent and othermaterials, if any, and the amount of each comprising the coatingcomposition. Employing a volatile organic content of about 430 g/l (3.6lb./gal.) and selecting preferred components as described above, thebake time and temperature is typically about 15 to about 30 minutes andabout 135° C.-165° C. (275° F.-325° F.), respectively. The coatingcompositions according to preferred embodiments of the invention, asdescribed above, have been found to provide the best coating resultswhen cured at temperature at about 150° C. (300° F.) for 20 minutes. Itis a highly significant advantage of the invention, however, that thesesame coating compositions can withstand, for example, temperature ashigh as about 200° C. (390° F.) for periods of time as long as about 60minutes. Thus, as noted above, great flexibility is provided in bothdesigning and implementing a curing schedule for parts coated with thecoating compositions of the invention. Thus, in the assembly ofautomotive vehicles, for example, vehicles unavoidably held in a curingoven for long periods of time during unplanned assembly line shut-downsare recovered with cured and unharmed coatings.

High solids coating compositions according to the present invention,comprising the preferred epoxy ester resins described above, melaminecrosslinking agent, for example, hexamethoxymethyl melamine, andpreferred polymeric catalyst have been found to afford cured coatingswith corrosion resistance comparable to conventional epoxy ester based,low solids sprayablecoating compositions. The significant reduction involatile organic content presents, therefore, a highly advantageousadvance in the art.

A most preferred use of the coating composition of the invention is as ahigh solids sprayable primer for use on a bare metal substrate such as ahousehold or industrial applicance housing or an automotive vehiclebody. Primer compositions typically are pigmented and any pigmentscommonly included in primer compositions for metal substrates andacrylic dispersion topcoats such as, for example, carbon black, ironoxide, lithopone, magnesium, silicate, silica, barium sulfate, TiO₂,chrome yellow, calcium chromate, strontium chromate, zinc potassiumchromate any the like may be used. The primer can be pigmented accordingto known methods including, for example, by grinding pigments in aportion of the curable resin and adding to the primer composition.

The pigment-to-binder ratio of the primer may be as much as 4:1 byweight, respectively, depending, in part, upon the condition of themetal substrate. It is preferred, however, to use a primer having apigment-to-binder ratio of about 1:1-2:1 by weight, respectively.

No special expedients are necessary in formulating the primercompositions of this invention. For example, they may be prepared simplyby incorporating the resinous components in a suitable solvent system.Thus, for example, by suitable mixing or agitation, each resinouscomponent may be dissolved in a solvent and the resulting solutionscombined to form finished primer compositions.

The solvent system may be any suitable combination of organic solventsas described above. For a high solids, sprayable, automotive vehicleprimer, the solvent will comprise preferably about 25 to about 35percent by weight of the total coating compositions, although of course,larger or smaller amounts may be utilized depending upon the solidscontent desired. For example, it may be desirable to formulate theprimer with a relatively high solids content and then reduce it tospraying consistency prior to the time of application.

The metal substrate can be, for example, aluminum, steel, or phosphatedcold-rolled steel. However, any metal used as a construction material isusable. The primer composition may be coated onto the metal base in anyconventional manner such as roll coating, brushing, curtain coating,etc. The preferred method of applying the primer composition to themetal is by spraying. The primer is cured at elevated temperatures byany convenient means such as baking ovens or banks of infra-red heatlamps. Suitable curing temperatures are discussed above.

The primer is generally thinned to from about 60 to about 70 percentsolids content for spraying purposes with conventional thinners such asaromatic hydrocarbons, commercial petroleum cuts which are essentiallyaromatic, and the like, and sprayed onto the metal base and cured. Theprimer is cured at elevated temperatures by any convenient means such asbaking ovens or banks of infra-red heat lamps. Suitable curingtemperatures are as described above.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that the specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" are intended tomean parts by weight.

EXAMPLE I

This example illustrates the preparation of an epoxy ester resin for usein a coating composition according to the present invention. In asuitable reactor were charged 911 parts of Epon 829 (trademark) ShellChemical Company (diglycidyl ether of bisphenol-A), 564 parts of Empol1014 (trademark) Emery Industries, Inc., and 728 parts of Soya fattyacid. The temperature of the mixture was brought up to about 177° C.(350° F.) at which point an exothermic reaction took place that raisedthe temperature up to about 193° C. (380° F.). After 2 hours at thistemperature, the acid number was found to be 5.2. The reaction mixturewas then cooled down to about 149° C. (300° F.) and 275 parts of methylamyl ketone amd 275 parts of Cellosolve Acetate were added. Theresulting resin had a viscosity of W1/2 at 80% solids.

EXAMPLES II-V

Epoxy ester resins for use in coating compositions according to theinvention were prepared in the manner generally of Example I. Thecomponents employed are shown in Table I, below. The diepoxide, fattyacid and dicarboxylic acid, with catalyst (sodium carbonate), if any,were charged in a suitable reactor. The mixture was heated to about 177°C. (350° F.). At this point, exothermic reaction took place that broughtthe temperature to about 188°-199° C. (370°-390° F.). The reaction wascontinued at this temperature until the acid number dropped below 6.Then the product was cooled down to about 121° C. (250° F.) and thinnedto 80% non-volatiles by weight with methyl amyl ketone. In Table I, allamounts are shown in parts by weight.

                  TABLE I                                                         ______________________________________                                                   Example                                                                       II     III      IV       V                                         ______________________________________                                        Epon 829.sup.1                                                                             500      500                                                     DER 333.sup.2                  500                                            Epon 828.sup.3                        500                                     Empol 1016.sup.4                                                                           309      309      309    309                                     Linseed Fatty Acid                                                                         400                                                              Pamolyn 200.sup.5     400                                                     Soya Fatty Acid                400    400                                     Sodium Carbonate                      0.5                                     Methyl Amyl Ketone                                                                         300      300      300    300                                     % Non-Volatiles                                                                            80.0     79.8     79.6   79.8                                    Viscosity    X        X        Y      Y1/2                                    Acid Number  5.2      4.8      5.6    5.8                                     ______________________________________                                         .sup.1 Trademark, Shell Chemical Co. (diepoxide; specifically, bisphenolA     epichlorohydrin epoxy resin)                                                  .sup.2 Trademark, Dow Chemical Co. (diepoxide)                                .sup.3 Trademark, Shell Chemical Co. (diepoxide)                              .sup.4 Trademark, Emery Industries, Inc. (dimer acid)                         .sup.5 Trademark, Hercules Incorporated, Wilmington, Delaware (pale,          colorstable high purity grade linoleic acid)                             

EXAMPLE VI

Epoxy ester resin for use in a coating composition according to theinvention is prepared in the manner generally of Example I. Thecomponents employed are Epon 829 (trademark), Shell Chemical Company,500. g, azelaic acid, 109. g, and Soya fatty acid, 400. g. Thediepoxide, fatty acid and dicarboxylic acid are charged in a suitablereactor. The mixture is heated to about 177° C. (350° F.) at which pointexothermic reaction brings the temperature to about 188°-199° C.(370°-390° F.). The reaction is continued at this temperature until theacid number drops below 6. The product is then cooled to about 121° C.(250° F.) and thinned to about 78.1% non-volatiles by weight with 284. gmethyl amyl ketone. The resin has viscosity of Y1/2 and acid number of4.6.

EXAMPLE VII

An epoxy ester resin according to the invention is prepared by chargingin a suitable reactor 622 parts of Araldite RD-2 (trademark) Ciba-GeigyCorporation (diglycidyl ether of 1,4-butane diol), 564 parts of Empol1014 Emery Industries, Inc., 728 parts of Soya fatty acid and 1.0 partsof sodium carbonate. The temperature of the mixture is brought up toabout 177° C. (350° F.) at which point an exothermic reaction takesplace that raises the temperature up to 193° C. (380° F.). After onehour at this temperature, the acid number is found to be about 5.2. Thereaction mixture is then cooled down to about 149° C. (300° F.) and 500parts of methyl amyl ketone were added. The resulting resin has aviscosity of R at 80% solids.

EXAMPLES VIII-X

This example illustrates the prepartion of polymeric catalyst for use ina coating composition according to the present invention. The monomercomponents and t-butyl perbenzoate initiator, in the amounts shown inTable II, below, were combined with a small quantity of methyl amylketone solvent and added over a five hour period into refluxing methylamyl ketone containing cumene hydroperoxide polymerization initiator.Following completion of the addition, the mixture was maintained at 149°C. (300° F.) for about one hour. The mixture of Example IX and ofExample X each was then stripped of solvent to the desired solids level,as listed in Table II. The viscosity and acid number of the polymericcatalyst product are shown in Table II. All component amounts are shownin parts by weight.

                  TABLE II                                                        ______________________________________                                                       Example   Example   Example                                    Composition    VIII      IX        X                                          ______________________________________                                        Methyl-amyl Ketone                                                                           1500      1500      1500                                       Butyl Methacrylate                                                                           1050      1050      --                                         Butyl Acrylate --        --        150                                        Styrene        --        150       --                                         Acrylic Acid   450       300       450                                        t-Butyl Perbenzoate                                                                          67        67        67                                         Cumene Hydroperoxide                                                                         37        37        37                                         Solids (% by weight)                                                                         50        80        75                                         Viscosity      L         Z.sub.7   Z.sub.4                                    Acid Number    238       152       235                                        ______________________________________                                    

EXAMPLE XI

A millbase, that is, a composition pigment paste was prepared bygrinding in a ballmill the following mixture:

    ______________________________________                                        Composition      Parts                                                        ______________________________________                                        Barium Sulfate   1626                                                         Red Iron Oxide   60                                                           Titanium dioxide 105                                                          Silica           75                                                           Strontium chromate                                                                             99                                                           Polyethylene Wax 48                                                           Xylene           200                                                          Toluene          240                                                          2 ethyl hexanol  57                                                           Resin of Example V                                                                             264                                                          ______________________________________                                    

EXAMPLES XII-XIII

Coating compositions according to the invention were prepared, eachbeing adapted for use as a high solids, sprayable, pigmented primer forapplication over bare, unpolished steel automotive vehicle body panelsin an automotive vehicle assembly operation. The coating compositioncomponents are shown in Table III, below. It should be noted that use ofa drier is optional to catalyse reaction of fatty acid double bonds toprovide additional crosslinking in the cured resin. In Table III, allcomponent amounts are expressed in parts by weight.

                  TABLE III                                                       ______________________________________                                                           Example                                                                       XII   XIII                                                 ______________________________________                                        Epoxy Ester Resin    248     248                                              of Example I                                                                  Polymeric Catalyst of                                                         Example VIII         24      --                                               Example X            --      23                                               Millbase of Example XI                                                                             801     800                                              Resimine 717.sup.1   110     110                                              6% Manganese Naphthanate                                                                           4       4                                                (Drier)                                                                       Butanol              35      35                                               ______________________________________                                         .sup.1 Trademark, Monsanto Co., St. Louis, MO. (low temperature, high         solids methylated melamineformaldehyde resin crosslinking agent).        

EXAMPLE XIV

The coating composition of Examples XII and XIII are spray applied tobare, unpolished Bonderite steel, cured, and tested for corrosionresistance and humidity resistance. The curing schedule for each coatingcomposition is 135° C. for 15 minutes. Corrosion resistance, measured asinches of corrosion from scribe line following 240 hours salt spray, andhumidity resistance, qualitatively evaluated following exposure tocondensing humidity at 43° C. (110° F.), is found to be excellent foreach of the coating compositions.

EXAMPLE XV

The following example illustrates the preparation of a coatingcomposition of the present invention and, in particular, illustrates thehot blend method of mixing the polymeric catalyst with the epoxy esterresin. In a suitable reactor are charged 248 parts of resin of Example Iand 33 parts of resin of Example VII. The mixture is heated up to 104°C. (220° F.) and stirred at this temperature for 2 hours. After the twohour period the mixture is cooled to room temperature and was added to apreviously prepared mixture containing 800 parts of millbase of ExampleXI, 100 parts of Resimine 717 (trademark, Monsanto Company, St. Louis,Mo.), 4 parts of 6% manganese naphthanate drier, 35 parts of butanol, 3parts of polybutyl acrylate and 15 parts of Butyl Cellosolve Acetate(trademark, Union Carbide Corporation, New York, N.Y.) The mixture issubsequently thinned with methyl amyl ketone to a viscosity of about 18seconds, #4 Ford Cup at 27° C. A number of unpolished Bonderite steelpanels are sprayed and baked at different temperatures (bakingschedules: 250° F.×15 mins.; 275° F.×15 mins.; 300° F.×20 mins.; 325°F.×30 mins.; 380° F.×60 mins.). Corrosion resistance of the panels afterexposure to salt spray tests for 240 hrs. is found to be excellent.Additional panels, coated and baked at the schedules shown above andthen top-coated with white enamel, exhibit excellent humidityresistance, chip resistance and adhesion (gravelometer tests). The abovecoating composition, after 16 hrs. at 60° C. (140° F.) shows only 2seconds increase in viscosity (#4 Ford Cup) and, after 5 days at 60° C.(140° F.), shows only 5 seconds increase.

EXAMPLES XVI-XXII

Coating compositions according to the present invention are suitablyprepared according to the method of Example XV employing components inthe amounts shown in Table IV, below. In each case, the properties ofthe coating composition and of the cured coating made therefrom,specifically storage stability of the coating composition and corrosionresistance, humidity resistance, chip resistance and adhesion of thecured coatings, are found to be excellent, except that the storagestability of the coating composition of Example XXII is less due to theuse therein of phenyl acid phosphate (i.e., non-polymeric) catalyst.

                                      TABLE IV                                    __________________________________________________________________________                  Example                                                                       XVI XVII                                                                              XVIII                                                                             XIX XX  XXI XXII                                                                              XXIII                               __________________________________________________________________________    Millbase of Example X                                                                       800 800 800 800 800 800 800 800                                 Epoxy ester resin of                                                          Example I     248                     248                                     Example II        248                                                         Example III           248                                                     Example IV                248                                                 Example V                     248                                             Example VI                        248                                         Example VII                               248                                 Polymeric catalyst of                                                         Example VIII      35          35  35  35  35                                  Example IX    30      25                                                      Example X                 25                                                  Phenyl acid phosphate                 1                                       Resimine 717.sup.1                                                                          110 110         110 110 110 110                                 Cymel 325.sup.2       110 110                                                 6% Manganese Naphthenate                                                                    4   4   4   4   4   4   4   4                                   Butanol       40  35  40  35  40  40  40  40                                  Butyl Cellosolve Acetate.sup.3                                                              15  15  15  15  15  15  15  15                                  Polybutylacrylate                                                                           3   3   3   3   3   3   3   3                                   __________________________________________________________________________     .sup.1 Trademark, Monsanto Co., St. Louis, MO. (low temperature, high         solids methylated melamineformaldehyde resin crosslinking agent).             .sup.2 Trademark, American Cyanamid Company, Wayne, New Jersey (highly        methylated melamine formaldehyde resin).                                      .sup.3 Trademark, Union Carbide Corporation, New York, New York (ethylene     glycol monobutyl ether acetate)                                          

In view of this disclosure, many modifications of this invention will beapparent to those skilled in the art. It is intended that all suchapparent modifications fall within the true scope of this invention andbe included within the terms of the appended claims.

INDUSTRIAL APPLICABILITY

It will be apparent from the foregoing that this invention hasindustrial applicability as a coating composition, especially as a highsolids primer coat composition for automotive vehicles, householdapplicances and the like, and other applications where the coatingcomposition desirably has excellent storage stability and the curedcoating desireably provides excellent humidity and solvent resistance toprotect a substrate, for example a metal substrate, against corrosion,wear and the like.

What is claimed is:
 1. A novel, organic solvent based, thermosettingcoating composition comprising:A. epoxy ester resin of number averagemolecular weight (M_(n)) about 1000 to about 5000, being the reactionproduct of diepoxide with (i) dicarboxylic acid in chain extensionreaction and (ii) monobasic fatty acid in chain terminatingesterification reaction, which chain extension and esterificationreactions occur substantially simultaneously at a reaction temperaturereaching at least about 135° C., wherein the epoxy functionality,dicarboxylic acid carboxyl functionality and fatty acid carboxylfunctionality are employed in relative proportions of about1:0.3-0.8:0.3-0.8 equivalents, respectively; B. polyfunctionalaminoplast crosslinking agent; and C. polycarboxy functional polymericcatalyst of number average molecular weight (M_(n)) about 1,000-10,000being substantially unreactive at room temperature with the epoxy esterresin and the polyfunctional aminoplast crosslinking agent, in an amountof about 2% to about 15% by weight of resin solids in the coatingcomposition.
 2. The solvent based, thermosetting coating composition ofclaim 1, wherein said epoxy ester resin number average molecular weightis about 1000 to about
 3000. 3. The solvent based, thermosetting coatingcomposition of claim 2, wherein said diepoxide has a number averagemolecular weight of about 100-1000.
 4. The solvent based, thermosettingcoating composition of claim 1, wherein said diepoxide is selected fromthe group consisting of bisphenol-A epichlorohydrin epoxy resin,hydantoin epoxy resin, cyclic and acyclic aliphatic diepoxide, and thelike and a mixture of any of them.
 5. The solvent based, thermosettingcoating composition of claim 1, wherein said diepoxide bears twoterminal epoxide groups.
 6. The solvent based, thermosetting coatingcomposition of claim 1, wherein said diepoxide consists essentially ofdiglycidyl ether bisphenol-A resin.
 7. The solvent based, thermosettingcoating composition of claim 1, wherein the dicarboxylic acid has anumber average molecular weight of about 145-1000.
 8. The solvent based,thermosetting coating composition of claim 1 or 6, wherein saiddicarboxylic acid is saturated or unsaturated, cyclic or acyclicaliphatic or aromatic dicarboxylic acid or a mixture thereof.
 9. Thesolvent based, thermosetting coating composition of claim 1, whereinsaid dicarboxylic acid is of the general formula:

    HOOC--R--COOH

wherein R is a divalent linking moiety substantially unreactive with theepoxy functionality of the diepoxide resin.
 10. The solvent based,thermosetting coating composition of claim 9, wherein R is selected fromthe group consisting of a straight or branched alkylene or alkylidenemoiety of about 4 to about 42 carbons and the like and a mixturethereof.
 11. The solvent based, thermosetting coating composition ofclaim 1, wherein said dicarboxylic acid provides two terminal carboxylgroups.
 12. The solvent based, thermosetting coating composition ofclaim 1, wherein said dicarboxylic acid consists essentially ofsubstantially saturated, acyclic, aliphatic dimer acid of about 4-42carbons.
 13. The solvent based, thermosetting coating composition ofclaim 1, wherein said dicarboxylic acid consists essentially of thedimer acid reaction product of C-18 fatty acid.
 14. The solvent based,thermosetting coating composition of claim 1, wherein said monobasicfatty acid is selected from the group consisting of fatty acids of about8 to about 18 carbons and a mixture of any of them.
 15. The solventbased, thermosetting coating composition of claim 1, wherein saidmonobasic fatty acid consists essentially of substantially saturated,acyclic, aliphatic fatty acid.
 16. The solvent based, thermosettingcoating composition of claim 1, 6 or 13 wherein said monobasic fattyacid consists essentially of Soya fatty acid.
 17. The solvent based,thermosetting coating composition of claim 16, wherein saidpolyfunctional aminoplast crosslinking agent consists essentially ofhexa(methoxymethyl)melamine or the like or a compatible mixture thereof.18. The solvent based, thermosetting coating composition of claim 16,wherein said diepoxide, said dicarboxylic acid and said fatty acid areemployed in relative amounts of about 1:0.4-0.6:0.4-0.6 equivalents,respectively.
 19. The solvent based, thermosetting coating compositionof claim 1, wherein said polycarboxy functional polymeric catalyst has anumber average molecular weight (M_(n)) about 1,500-3,000.
 20. Thesolvent based, thermosetting coating composition of claim 1, 6, 13 or 15wherein said polycarboxy functional polymeric catalyst comprises thereaction product of (i) ethylenically unsaturated carboxylic acid, with(ii) ethylenically unsaturated copolymerization monomer which providesto said reaction product no functionality substantially reactive at roomtemperature with said epoxy ester resin or said polyfunctionalaminoplast crosslinking agent.
 21. The solvent based, thermosettingcoating composition of claim 20, wherein said carboxylic acid isselected from the group consisting of acrylic acid, methacrylic acid,butanoic acid and the like and a compatible mixture of any of them. 22.The solvent based, thermosetting coating composition of claim 21,wherein said copolymerizable monomer is selected from the groupconsisting of glycidyl acrylate, glycidyl methacrylate, styrene, vinylether and the like or a compatible mixture of any of them.
 23. Thesolvent based, thermosetting coating composition of claim 20, whereinsaid polycarboxy functional polymeric catalyst consists essentially ofthe reaction product of about 20-45% by weight of said carboxylic acidmonomers with about 55-80% by weight of said copolymerization monomers.24. The solvent based, thermosetting coating composition of claim 23,wherein said polycarboxy functional polymeric catalyst consistsessentially of the polymerization reaction product of about 30% byweight acrylic acid with about 70% by weight butyl methacrylate.
 25. Thesolvent based, thermosetting coating composition of claim 1, whereinsaid polycarboxy functional polymeric catalyst is used in an amount ofabout 5% to about 10% by weight of resin solids in the coatingcomposition.
 26. The solvent based, thermosetting coating composition ofclaim 1, wherein said polycarboxy functional polymeric catalyst is usedin an amount sufficient to raise the acid level of the epoxy ester resinto about 15 to about
 35. 27. The solvent based, thermosetting coatingcomposition of claim 16, wherein said polycarboxy functional polymericcatalyst is mixed with the epoxy ester resin at a temperature at orabove about 105° C.
 28. A sprayable, pigmented high solids primeradapted for use on bare metal substrate, comprising the coatingcomposition of claim 1, 6, 13 or 15 wherein the volatile organic contentis less than about 400 g/l and the viscosity no greater than about 35sec., #4 Ford Cup at 27° C.
 29. The sprayable, pigmented, high solidsprimer of claim 28 wherein the pigment to resin ratio is about 1:1 toabout 2:1, respectively.
 30. A novel, organic solvent based,thermosetting coating compositions comprising:A. epoxy ester resin ofnumber average molecular weight (M_(n)) about 1000 to about 3000, beingthe reaction product of diepoxide, consisting essentially of diglycidylether bisphenol-A resin, with (i) dicarboxylic acid consistingessentially of the dimer acid reaction product of C-18 fatty acid, inchain extension reaction, (ii) monobasic fatty acid consistingessentially of Soya fatty acid, in chain termination esterificationreaction, and (iii) catalyst for said chain extension and esterificationreactions, which reactions occur substantially simultaneously at areaction temperature reaching at least about 135° C., wherein the epoxyfunctionality, dicarboxylic acid carboxyl functionality and fatty acidcarboxyl functionality are employed in relative proportions of about1:0.4-0.6:0.4-0.6 equivalents, respectively; B. polyfunctionalaminoplast crosslinking agent; and C. polycarboxy functional polymericcatalyst of number average molecular weight (M_(n)) about 1,000-10,000being substantially unreactive at room temperature with the epoxy esterresin and the polyfunctional aminoplast crosslinking agent, in an amountof about 2% to about 15% by weight of resin solids in the coatingcomposition.
 31. A sprayable, pigmented, high solids primer adapted foruse on bare metal substrate, comprising the coating composition of claim30 wherein the volatile organic content is less than about 400 g/l andthe viscosity no greater than about 35 sec., #4 Ford Cup at 27° C.